Apparatus and method for dressing grinding wheels

ABSTRACT

Method and apparatus for truing or dressing a grinding wheel which is rotated at a progressively increasing angular velocity to compensate for decreasing wheel diameter so that a constant peripheral wheel speed is maintained, the speed of traverse of the dressing tool along the grinding face of the wheel is controlled in accordance with wheel diameter. This is achieved by means responsive to any change in the radial position of the dressing tool with respect to the wheel axis, and controlling the traverse speed of the truing tool accordingly, so that for a particular sequence of repetitive grinding operations the traverse speed is inversely proportional to the wheel diameter, whereby the grinding face is repeatedly dressed to substantially a uniform surface finish during the useful life of the grinding wheel.

Stevens 'Oct.9,1973

[ APPARATUS AND METHOD FOR DRESSING GRINDING WHEELS [75] Inventor: Thomas F. Stevens, Shrewsbury,

Mass.

[73] Assignee: The Warner & Swasey Company,

Cleveland, Ohio [221 Filed: July 8,1971

21 Appl.No.: 160,867

[52] US. Cl 125/11 PH, 51/165187 [51] Int. Cl B24!) 53/08 [58] Field of Search l25/ll R, vll CW,

125/11 PH, 11 TP, 11 H, 11 NT; 5l/l69.87

[56] References Cited UNITED STATES PATENTS 7 2,648,172 8/1953 Silven 51/5 2,697,426 12/1954 Price et al. l25/ll'PH 3,033,187 5/1962 Wespi 125/11 cw 3.429.305 2/1969 Hall 125/11 R Primary Examiner-Harold D. Whitehead Assistant Examiner--N. P. Godici Attorney-Thomas L. Tarolli and Calvin G. Covell [57] ABSTRACT Method and apparatus for truing or dressing a grinding wheel which is rotated at a progressively increasing angular velocity to compensate for decreasing wheel diameter so that a constant peripheral wheel speed is maintained, the speed of traverse of the dressing tool along the grinding face of the wheel is controlled in accordance with wheel diameter. This is achieved by means responsive to any change in the radial-position of the dressing tool with respect to the wheel axis, and controlling the traverse speed of the truing tool accordingly, so that for a particular sequence of repetitive grinding operations the traverse speed is inversely proportional to the wheel diameter, whereby the grinding face is repeatedly dressed to substantially a uniform surface finish during the useful life of the grinding wheel.

19 Claims, 5 Drawing Figures PATENTEDUBT 91m 3,763,844

INVENTOR. THoM AS F. STEVENS BACKGROUND OF THE INVENTION 1. Field of lnvention This invention relates generally to precision grinding machines of the kind used to perform identical repetitive grinding operations on a series of workpieces, and in which the grinding wheel is rotated about an axis at a progressively increasing angular velocity in accordance with decreasing wheel diameter so as to maintain a constant peripheral wheel speed. The invention relates particularly to a method and device for dressing or truing of grinding wheels in such machines.

2. Description of the Prior Art In the art of grinding it is well known that proper wheel truing or dressing is an important factor in determining the load on the grinding wheel, the surface finish of the ground workpieces, the rate of removal of waste material, and the grinding ratio, and that the condition or finish of the dressed face of the wheel depends .upon'the velocity of traverse of the dressing tool across the wheel face. Hitherto it has been the common practice first to determine the optimum dressing'speed for a particular grinding operation and thereafter let the dressing speed remain fixed. This practice has certain disadvantages for as the wheel diameter decreases, the fixed speed changes the truing tool pitch pattern and hence the condition of the wheel surface if the peripheral wheel speed is maintained constant, and so the optimum dressing condition is not maintained. Further- .more, there is an ever-increasing loss of production time as the work proceeds owing to the necessity of dressing the wheel more frequently as its diameter decreases.

US. Pat. No. 2,409,240 issued Oct. 15, i946 discloses a method and apparatus whereby different preformed portions of an annular or cup type grinding wheel, for grinding spiral bevel and hypoid gears, are dressed with a plurality of dressing tools traversed at different constant rates for the purpose of providing different degrees of surface finish on the preformed portion of the wheel. Also disclosed is the known fact that as the traverse rate increases, the lead or pitch of the helix generated by the truing tool increases and the coarser the finish of the dressed surface becomes. Conversely, a slow traverse rate will produce a decrease in the pitch and a finer finish on the dressed surface, and a traverse rate that is to slow produces to fine a finish causing the wheel to burn the work.

However, the initial size of the preformed annular cup type wheel and portions thereof are not reduced diameterically as in the applicant's invention; but instead are reduced axially and all portions rotate at the same constant speed with no change fromthe initial peripheral surface speed during the life of the annular wheel. Therefore, there was no need to vary the traverse rate of any one of the dressing tools to maintain a constant pitch of the dressing tool and hence a uniform finish on the dressed surfaces of the wheel.

The present invention is based on the realization that in order to maintain the optimum dressing condition or surface finish on the wheel as the work proceeds, it is necessary to increase the velocity of traverse of the dressing tool as the wheel diameter decreases and vice versa. The velocity of traverse should, in fact, be directly proportional to the angular velocity of the wheel,

that is to say, inversely proportional to the wheel diameter.

SUMMARY OF THE INVENTION A method and device for truing a grinding wheel of a grinding machine having variable wheel drive means for maintaining a constant peripheral surface speed of the grinding wheel face. The truing device and method comprises adjustable control means such as a variable fluid flow control valve or a rheostat adjusted by means movable with and'responsive to the radial distance and movement of the truing or dressing tool relative to the axis of rotation of the grinding wheel to regulate and change the speed respectively of either a reversible fluid motor or a reversible electric motor operatively connected to traverse a truing tool slide and the dressing tool together axially along the peripheral grinding face of the wheel. The speed control means is adapted for use with conventional straight, and form truing devices, with' or without form bars to guide the path of the truing tool. A movable control member of the adjustable speed control means is connected to the truing tool support which is progressively advanced in predetermined increments for truing the wheel by either an automatic or a hand operated reversible truing tool feed mechanism, toward the axis of the wheel. The movable control member is adjustable relative to the truing tool support and a fixed member of the speed control means for the purpose of initially setting and calibrating the speed control means so the truing toolproduces the desired truing tool pitch pattern and surface finish on the grinding face of the wheel. Thereafter the progressive incremental feed movements of the truing tool toward the wheel axis causes a corresponding number of progressive incremental movements of the movable member relative to the fixed member of the speed control means which progressively increases the traverse speed of the truing tool as the diameter and radius of the wheel is progressively decreased-by the truing tool. Hence the initial predetermined desired truing tool pitch pattern, texture or finish is maintained on the grinding wheel face. Similarly, the speed control means is utilized to vary the traverse speed of a form or profile truing device adapted with a pattern or form bar, a follower fixed to the truing tool support movable radially in response to the contoured surfaces and shape of the form bar to be reproduced by the truing tool on the grinding wheel face. The truing tool is first advanced a predetermined increment'radially toward the axis of the wheel to true and reduce the size of the wheel. However, as the truing tool slide is traversed axially the form bar causes varying amounts of radial movement of the follower and the truing tool toward and away from the grinding wheel axis. Hence, the speed control means automatically varies the traverse movement of the truing tool and maintains the desired uniform truing tool pitch pattern texture or surface finish on the contoured or formed grinding wheel face in accordance with changes in radial position of the truing tool relative to the axis of rotation of the wheel. The speed control means is adapted to vary the traverse speed of the truing tool at a rate which is inversely proportional to the radial distance of the truing tool from the rotational axis of the grinding wheel.

Accordingly it is one object of the invention to provide a method of dressing a grinding wheel in a precision grinding machine wherein the grinding wheel is rotated about an axis at a progressively changing angularvelocity in accordance with progressively changing wheel diameter so as to maintain a constant peripheral surface speed of the grinding face, which method comprises positioning a dressing tool at a predetermined radial distance from the rotational axis of the wheel and in operative relation to true the peripheral grinding face and thereby reduce the diameter of the wheel; and simultaneously adjusting speed control means in response to the radial movement of the dressing tool to control and vary the speed of the truing tool along the peripheral grinding face at a rate that is inversely proportional to the radial distance, and traversing the dressing tool in an axial direction along the peripheral grinding face at the speed inversely proportional to the radial distance of the dressing tool from the axis of wheel rotation.

Another object of the invention is to provide a truing device adapted to carry out the method in a grinding machine of the kind referred to above comprising means for supporting the dressing tool radially of and in operative relation to true the peripheral grinding face of the grinding wheel, means for positioning the dressing tool at progressively lesser radial distances from the rotational axis the wheel to dress or true and thereby progressively reduce the diameter of the wheel, means for traversing the dressing tool along the peripheral grinding face in the direction of the rotational axis of the wheel, and speed control means for determining the' speed of traverse of the dressing too] including a control element movable with and responsive to the radial position of the dressing tool relative to the rotational axis for controlling and varying the speed regulating means to control the traverse speed of the dressing tool as a predetermined function of the radial position and produce a substantially constant surface finish on the grinding face as the diameter of the wheel is reduced and the angular velocity of the wheel is increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic representation of a dressing apparatus according to the invention, the apparatus employing a reversible linear fluid motor; and a variable fluid flow control valve for regulating the speed of the fluid motor.

FIG. 2 is a diagrammatic representation of a second dressing apparatus according to the invention, the apparatus employing a reversible electric motor and a rheostat for regulating the speed of the electric motor.

FIG. 3 is a partial view of a modified form of the invention showing how a reversible rotary fluid motor may be substituted for either the electric motor in the apparatus shown in FIG. 2, and how the gear reduction unit and the feed screw shown in FIG. 2 can be driven by the rotary fluid motor and substituted for the linear fluid motor in the apparatus shown in FIG. 1;

FIG. 4 is a partial view of another modification of the invention showing how either a fluid or an electric reversible rotary motor may be coupled directly to the feed screw shown in FIGS. 2 and 3.

FIG. 5 is a cross sectional view taken on line 55 of FIG. 1 showing the variable fluid flow control orifice in the speed control valve for the fluid motors.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS Each truing or dressing apparatus disclosed is diagrammatically shown, by way of example only, and is substantially a modified version of either of the truing devices disclosed, in US. Pat. Nos. 2,647,504 and 2,900,974 issued on Aug. 4, 1953 and Aug. 25, 1959 respectively and to which reference may be had for details not disclosed herein. The invention is also applicable to other conventional types of truing or dressing devices such as disclosed in US Pat. Nos. 2,648,171 and 2,648,172 both of which issued Aug. 11, 1953. Additionally, US. Pat. No. 2,648,172 discloses means primarily for automatically maintaining a uniform peripheral surface speed of the wheel. Similar constant peripheral speed control means are incorporated and diagrammatically shown in FIGS. 1 and 2 of the instant invention. However, any suitable grinding wheel speed control means may be used some of which are disclosed inU.S. Pat. Nos. 2,642,703 and 2,746,214 which issued on June 23, 1953 and May 22, 1956 respectively.

Each apparatus shown is adapted for use in a precision grinding machine having a cylindrical grinding wheel X, the grinding wheel being mounted on a shaft Y for rotation about an axis Z-Z. The grinding machine in each case is of the kind in which the wheel X is rotated about the axis Z-Z at a progressively increasing or changing angular velocity or revolutions per minute in accordance with decreasing or changing wheel diameter by a variable speed wheel drive motor M regulated by speed control means such as a rheostat V operatively connected by suitable gearing to the truing tool feed mechanism. The angular velocity being inversely proportional to the wheel diameter so that the peripheral surface speed of the grinding wheel face is maintained substantially constant. The peripheral grinding face of the wheel X is dressed intermittently or periodically by means of a conventional dressing tool 10 such as, a diamond nib which, in accordance with the present invention, is traversed longitudinally along the grinding face in the axial direction at a speed which is proportional to the angular velocity of the wheel, that is, inversely proportional to the wheel diameter.

In the dressing apparatus shown in FIG. I, the dressing tool 10 is carried at the lower end of a radially or transversely movable truing tool carrier or shaft 1 l slidably mounted in a longitudinally movable tool carrier means which may include, as shown a transversely or radially movable slide 12 supported on a longitudinally or axially movable slide 14 or merely the longitudinally movable slide 14. The tool carrier 11 is held against rotation and has a threaded portion engaging a rotatable feed nut 133 held against axial movement. A truing tool feed mechanism TF such as disclosed in US. Pat. No. 2,900,974 is provided for rotating the nut and moving the tool carrier 11 relative to the transverse slide 12 and the axis ZZ so as to move the tool 10 into and out of engagement with the grinding face 13 of the wheel X. The longitudinally movable slide 14 with the transversely movable slide 12 thereon is constained to move in a longitudinal direction parallel to the axis Z-Z by means ofa conventional slideway 15 on which the slide 14 is mounted, the slideway being rigidly fixed to and supported by the structure of the grinding machine indicated at 15'.

Movement of the slide 14 in either direction along the slideway is effected by means of a reversible and variable speed linear. fluid motor 16. The motor 16 comprises a cylinder 17 whose axis extends parallel to the rotational axis Z-Z of the grinding wheel, and a piston 18 slidable in the cylinder. A rigid connector or piston rod 19 between the piston 18 and slide 14 ensures that the latter will move along the slideway in unison with the piston. Fluid under pressure is delivered to the cylinder 17 of the motor 16 via a supply line 20, which is selectively connectible to either one of a pair of conduits leading to ports at opposite ends of the cylinder by means of a directional control valve 21. The setting or position of the control valve 21 determines the direction in which the piston 18, and hence the toolcarrier, will move when fluid under pressure is supplied to the cylinder.

The fluid under pressure is delivered through a supply line 20 to the control valve 21 and then to the fluid motor from a fluid supply source or reservoir generally indicated at 22, by way of a pump P and fluid exhausts through valve 21 and a speed regulator or control valve 23. The speed control valve 23 comprises a valve housing 24 having an outlet port 25 connected to the reservoir 22 and an inlet port 26 connected to the exhaust port of valve 21. Slidable within the valve housing 24 is a spool 27 having a slot or orifice 28 of progressively increasing or constantly varying depth between the inlet and outlet ports. The slot 28 co-operates with a spring biased needle 29 to define an orifice or restriction whose effective area is detennined by the axial position of the spool 27 within the valve housing relative to the needle 29. The setting of the needle 29 may be adjusted by means of an adjusting screw 30.

The valve housing 24 is mounted on a bracket 31 which is rigidly mounted on the slide 14, and one end of the spool 27 has a rack 32 with gear teeth cooperating with actuating means comprising a pinion gear 33 meshing with the rack 32 and fixed to aportion of a shaft 34 rotatably supported in the housing 24. A portion of the shaft 34 extends out one side of the housing 24 and has a large drive gear 35 fixed to and rotatable therewith and the pinion gear 33. An adjustable drive rack bar 36 has gear teeth in mesh with the drive gear 35 and is adjustably fixed to an end of a guide strap,.

support or member 37 movable within a groove, slot or guideway in a bracket 38 for axial movement with the tool carrier 11. The rack for 36 is adjustable relative to the guide strap 37 and the tool carrier 11 by the provision of an adjusting screw and lock nut mechanism 39 shown for the purpose of calibrating and preadjusting the position of the spool 27 of the speed control valve 23 with the initial diameter and constant peripheral speed of the grinding wheel.

As the truing tool is fed or moved radially by the tool carrier 11 the rack bar 36 also slides a corresponding amount along a slideway on one side of the bracket 38 and rotates the drive gear 35 which in turn rotates shaft 34 and the pinion gear 33 a portional amount and lesser number of teeth. Rotation of the pinion gear 33 moves the spool 27 relative to the needle 29 and varies the size of the orifice accordingly to vary the traverse rate of the longitudinally or axially movable truing tool slide 14 and the truing tool 10 across the grinding face 13. Thus, the axial position of the spool 27, and hence the effective area of the valve orifice is determined by the radial distance R of the dressing tool 10 from the rotational axis Z-Z. In practice the depth of the slot 28 increases uniformly along its length, so that the effective area'of the valve orifice, and hence the driving speed of the fluid motor, is an inverse linear function of the radial distance R of the dressing tool from the axis Z-Z, that is to say an inverse linear function of the wheel diameter.

It will be noted that when the optimum dressing speed has been determined for a particular repetitive grinding operation, the needle 29 having been set by the adjusting screw- 30, the optimum conditions will be maintained in subsequent dressing operations even though the grinding wheel diameter has decreased, for the peripheral surface speed of the grinding wheel face during each traverse of the dressing tool will remain constant.

The transversely or radially movable slide 12 is supported by spaced parallel slideways, not shown, to facilitate free movement of the slide 12 relative to the longitudinally movable slide 14. Fixed to the slide 12 is a follower 40 which is arranged to slide along an operative surface 41 of a forming bar 42. The forming bar is shaped so as to produce a surface of predetermined shape on the operative face 13 of the grinding wheel. In case a true cylindrical grinding face 13 as shown is desired on the periphery of the grinding wheel, a forming bar 42 is provided having a plane operative face. If an irregular shape is to be produced, such as, that shown in FIG. 2, the face 41 of the forming bar 42 is shaped to correspond with the shape to be produced on the periphery of the grinding wheel X.

The transversely movable slide 12 is preferably arranged to move radially relative to the path of movement of the longitudinally movable slide 14. The radial slide 12 is such that either its weight or other force applied to the slide 12 together with the parts carried thereby serves yieldingly to maintain the follower 40 in operative engagement with the forming bar 42 during the longitudinal movement of the slide 14. However in some instances the transverse or radial slide 12 may or may not be inclined as disclosed in US. Pat. No. 2,900,974 and conventional resilient means other than weight can be employed to bias and maintain the follower in engagement with the form bar 42. Slide 12 is moved relative to the longitudinally movable slide 14 due to the resultant thrust of the, follower 40 engaging the surface 41' of the forming bar 42' shown in FIG. 2 so that a vertical, angular, or curved surface may' be generated or trued on the peripheral operative grinding face of the grinding wheel X'in a manner similar to that disclosed in either of the US. Pat. Nos. 2,647,504 or 2,900,974.

As illustrated in FIG. 1 when the slide 14 is moved longitudinally, the follower 40 rides along a surface 41 on the forming bar 42 so as to true a cylindrical grinding face 13 on the grinding wheel. However, the follower 40 could be instead moving into engagement with either a curved, angled or radially extending face on another forming bar'such as shown in FIG. 2 whereupon continued movement of the slide 14 produces a thrust upon the slide 12 to move it generally in a radial direction so that the follower 40 and the truing tool 10 therewith follows the surface 41 to true a corresponding shape on the grinding wheel.

The opposite ends of the piston 18 are preferably of equal surface area but may have different surface area and therefore will travel at one speed as it moves to the right and at a different speed as it moves toward the left back to the initial starting position. However, the area of the opposite end faces of the piston 18 can be equalized by providing another piston rod 19a of the same cross sectional area as the piston rod 19 or extending the piston rod 19, as shown in FIG. 1. In some instances it may be desirable to first traverse the truing tool at a faster or rough truing rate on the first pass and at a slower or fine truing rate on the return or second finishing pass of the truing tool across the grinding face 13.

Therefore, in any desired arrangement or sequence of operation, it is obvious that the speed control valve 23 is preferably calibrated and connected into the fluid control system so that it dominates over any other throttle valve which may be utilized and determines the final traverse rate of the last or final finishing pass of the truing tool determining the desired surface finish on the grinding face and the workpiece ground thereby during each truing cycle.

The second dressing apparatus shown in FIG. 2 is basically similar to that of FIG. 1, and corresponding parts thereof are denoted by the same reference numerals. In this embodiment the tool carrier means or the longitudinal movable slide 14 is driven along the slideway at a predetermined speed by means of a reversible direct current electric motor 63 having a rotary output or drive shaft 64, the rotary output shaft being connected to drive the slide 14 through a speed reduction means 65 such as, a worm and worm gear shown coupled to a rotatable feed screw or screwthreaded shaft 66 which engages a conventional internally threaded nut, sleeve or collar not shown fixed to the slide 14. The feed screw 66 is journalled at its opposite ends in bearings 67, 68 carried by the slideway l5 and the fixed structure 15 of the grinding machine.

The motor 63 is preferably a direct current shunt motor. The speed of the motor is regulated by means of a speed regulating electrical circuit, the speed control means of which is a conventional rheostat 70 having usually a movable contact element engaging a resistance element to vary the resistance and electrical current to the motor. The setting of the rheostat, like the setting of the valve spool 27 in the preceding embodiment, is determined by the radial distance R of the dressing tool 10 from the axis ZZ. To this end the tool carrier 11 is connected by the rigid guide strap 37 to actuating means comprising a rack bar 72 which has gear teeth meshing with a drive gear 73 of a predetermined proportional diameter to provide the desired control of the rheostat 70. The gear 73 is rotatably mounted on the bracket 31 fixed to the slide 14 and operatively connected by any suitable means such as a flexible shaft to the rotary shaft and movable contact element of the rheostat 70. The rheostat is linearly wound, and therefore the motor supply current is an inverse linear function of the radial distance R of the tool 10 from the axis ZZ. The speed of motor 63 which determines the speed of traverse of the dressing tool 10, is therefore an inverse linear function of the diameter of the grinding wheel X. In order to calibrate or preset the dressing speed to produce the desired surface finish on the grinding face 13 of a wheel of given means of an adjusting screw mechanism 74, which interconnects the strap 37 and the rack 72.

As illustrated in the drawing, the motor supply lines are connected to the speed regulatory circuit by way of a reversing switch 76. Alternatively, however, the motor 63 may be unidirectional, reverse movement of the tool carrier being efiected by any suitable conventional reversing drive mechanism, such as, a reversible gearing not shown.

One example of applying the invention to form truing or dressing the grinding face 13 of the grinding wheel X is shown in FIG. 2 wherein a form bar 42' has a follower engaging surface 41' of different shape than that shown on the form bar 42 of FIG. I. The specific shape shown is only one example of the many possible shapes which may be reproduced on the grinding wheel face 13. The grinding wheel X formed to the shape shown has essentially a plurality of step like portions of differ ent diameters and radial distances from the axis Z-Z.

Thus, the truing tool I0, carrier 11, and rack 72 are moved radially various amounts toward and away from axis ZZ in response to the radial movement of the follower and the transversely movable slide 12 whereby the gear 73 and rheostat 70 are rotated various amounts in different directions to vary the traverse rate accordingly to produce and maintain the same or constant surface finish on each of the wheel portions of different diameter.

Referring to FIG. 3, there is shown a portion of the traversing mechanism disclosed in FIG. 2 driven by a conventional reversible rotary fluid or hydraulic motor RFM which may be substituted for either the reversible electric motor 63 or the reversible linear fluid or hydraulic motor 16, and connected to, operated and controlled by the speed control valve 23 in the manner disclosed in FIG. 1. It is obvious that each of the fluid conduits connected to the opposite ports of the linear fluid motor 16 can be reconnected to the operating ports of the rotary reversible fluid motor RFM suitably fixed to the slideway l5 and structure 15'. Shifting of the spool in the directional control valve 21 in one direction directs fluid under pressure to one or the other of the diameter and produce the optimum value for a particular sequence of grinding operations, the position of the rack 72 relative to the tool carrier 11 is initially set by ports in either one of the fluid motors utilized and traverses the slide 14 and the truing tool 10 in one direction. When the spool is shifted in the opposite direction the fluid is directed to the opposite port and reverses the directions of fluid flow to traverse the slide 14 and the truing tool 10 in the opposite direction.

Another modification is shown in FIG. 4 wherein a reversible rotary drive motor DM, which may be either the rotary fluid motor RFM or the electric motor 63 disclosed, is coupled directly to the traversing feed screw 66. Obviously, if the motor DM is of the fluid type it would be connected to and controlled by the control valve 23 in the system and manner disclosed in FIG. 1 and if electric, it would be connected to and controlled by the rheostat in the system and manner disclosed in FIG. 2.

In FIG. 5 there is shown in cross section an end of the spool 27 and the slot 28 which increases in depth at a predetermined progressively uniform rate and slope relative to the position of the needle valve 29. The slot 28 shown has V-shape surfaces mating with corresponding V- or cone-shape surfaces on the needle 29 which may be adjusted to provide between them the size orifice which determines the desired traverse rate of the slide 14.

In operation the speed controlled truing devices shown and described above are first preset or reset by turning the handwheel I07, pinion gear 106, feed gear 100, and feed nut 133 to retract the truing tool carrier 11 and the truing tool 10 away from the axis ZZ sufficiently to attach a new full size grinding wheel X onto the spindle Y of the grinding machine. Rotation of feed gear 100 and feed nut 133 rotates or causes rotary movement of pinion gear I08 operatively connected through suitable reduction gearing to reset the rheostat V and reduce the speed of the drive motor M to provide the desired initial predetermined constant peripheral surface speed of the wheel face 13. Retraction of the tool carrier 11 also resets the guide strap 37, the rack bars 36 and 72 which rotate the gears 33 and 35, and 73, to reset the spool 27 in valve 23 and the rheostat 70 respectively to slow down the reversible fluid motors 16 or RPM, and electric motor 63.

It is assumed that the speed control valve 23 and the rheostat 70 have been calibrated to the diameter of the wheel X by adjusting the position of rack bars 36 and 72 relative to the guide strap 37, truing tool carrier 11, and truing tool 10, and the needle 29 has been adjusted and fixed in position by the adjusting screw 30 to traverse the truing slide at the desired rate.

It is also assumed that the grinding wheel X is being driven by wheel drive means including motor M, power is available to line Ll, switch SW1 has been closed, and pump P is being driven and supplying fluid under pressure.

The truing tool 10 can now be advanced a predetermined increment toward the axis ZZ in any suitable well known manner such as by turning the handwheel 107 by hand or automatically actuating the truing tool feed mechanism TF in the manner disclosed in the US. Pat. No. 2,900,974. A predetermined amount or increment of rotation of the handwheel in the proper direction or actuation of the feed mechanism rotates the nut 133, fixed against axial movement about the screw threaded portion of the tool carrier 11 fixed against rotation, to feed the truing tool the desired amount toward the axis ZZ. Movement of the tool carrier 11 and the tool 10 causes a simultaneous corresponding movement of the rack bars 36 and 72 toward the axis Z--Z. Movement of the rack bar 36 toward the axis ZZ causes rotary movement of the gears 33 and 35 to shift spool 27 relative to the needle valve 29 to increase the size of the orifice an amount which will increase fluid flow and the speed of any of the fluid mo-. tors 16, or RFM to compensate for the subse-quent reduction in radius and diameter of the grinding wheel X. Simultaneous rotation of gear 100, 108, and rheostat V causes an increase in the speed of the motor M to compensate for what would otherwise cause a reduction in peripheral speed, due to a subsequent decrease in diameter, and radius of the grinding wheel X. Likewise movement of the rack bar 72 toward axis ZZ rotates gears 73 and 108 and hence rheostat 70 and V an amount which will increase the speed of electric motor 63 and M to compensate for the subsequent reduction in diameter, radius, and maintain a constant peripheral surface speed of and surface finish on the grinding wheel face.

The truing cycle is now ready to be performed in the usual manner and the various motor speed control devices have been calibrated or readjusted and preadjusted to maintain both the desired constant peripheral surface speed and constant surface finish of the grinding face regardless of the diameter and radius to which wheel is being dressed to grind workpieces.

Referring to FIG. 1, closing a switch SW2 either automatically or manually, energizes a solenoid S2 which shifts the spool in control valve 21 to the right. Fluid such as a hydraulic fluid under pressure from line or conduit 20 passes through a line or conduit connected to the left hand side or one side of either the reversible linear fluid motor 16 or rotary fluid motor RFM which may be substituted therefor and to the tool feed mechanism TF. Truing tool 10 is advanced an increment toward axis ZZ, valve 23 and rheostat V are readjusted accordingly before truing tool 10 contacts wheel face 13. The longitudinally movable slide 14 together with the speed control valve 23, transversely movable slide 12, follower 40, truing tool carrier II, and the truing tool 10 are traversed toward the right with the follower 40 in engagement with the surface 41 of the form bar 42. In this case the transversely movable slide 12, the truing tool carrier 11, and truing tool 10 carried thereby has no radial movement relative to slide 14 because the surface 41 of the form bar 42 is parallel to the 4 axis ZZ. Therefore, the truing tool 10 will pass axially over and dress the grinding face parallel to the axis ZZ at a speed controlled by the size of the orifice in valve 23. Fluid exhausts from the right hand end or opposite end of the linear fluid motor 16 or rotary motor RFM through the calibrated flow control orifice between V surfaces of the slot 28 and needle 29 of the speed control valve 21 to the reservoir 22. Movement to the right is arrested by either a stop not shown or bottoming of the piston 18 in cylinder 17.

The truing device operates in a similar manner to reverse the direction of traverse by either manually or automatically opening SW2 and closing SW3 to deenergize S2 and energize solenoid S3. Solenoid S3 shifts spool in valve 21 toward the left and directs fluid under pressure to the right hand end or opposite end of the fluid motor 16 or RFM. Valve 2 also, simultaneously a ctuates the feed mechanism TF, to advance the truing tool 10 toward axis ZZ which shifts the spool in valve 27 to increase the size of the orifice in valve 23 and readjusts the rheostat V. These movements increase the speed of either the fluid motors I6 or RPM and wheel drive motor M accordingly in the manner described to maintain the desired constant peripheral surface speed and dressed surface finish on the grinding wheel face I3.

Referring to FIG. 2 wherein the truing apparatus is provided with a contoured form bar 42 which may also be of the plain type shown in FIG. I. With form bar 42' the transversely movable slide l2 together with the truing tool carrier 11 and the truing tool 10 thereon will be moved toward and away from the axis ZZ in response to the radial movement of the follower 40 as it traverses over the contoured surface 41. Either the hand wheel 107 or feed mechanism TF is actuated as taught above to advance the tool 10 a predetermined increment toward axis ZZ which adjusts the rheostats V and to increase the speed of motors M and 63 accordingly.

Closing the F contacts of the reversing switch 76 connects L1 to rotate the motor 63 in one direction which rotates the gear reduction mechanism 65 and/or the feed screw 66 in a direction that traverses the slide 14 toward the right at a speed controlled by the rheostat 70. The rheostats 70 and V may be preadjusted or calibrated to any one of the initial different diameters to be trued on the grinding wheel X and both of the rheostats V and 70 will automatically be readjusted as the truing tool carrier 11 and truing tool moves radially in response to the movement of follower 40 to reproduce the form on the grinding face 13.

Thus any radial movement away from the axis Z-Z causes a corresponding simultaneous readjustment of the speed control devices disclosed to slow down the speed of the fluid or electric motors and the traverse rate of the slide 41 and the truing tool 10. Conversely any movement toward the axis ZZ readjusts the speed control devices to speed up the fluid and electric motors and the traverse rate of the slide and truing tool.

A truing cycle may consist of one or two passes of the truing tool over the grinding face of the grinding wheel. The first pass may be, if desired, a rough dressing and the second or return pass the finishing pass wherein the truing tool feed increment is less than that for rough dressing.

The truing apparatus shown in FIG. 2 may be reversed, after actuating the truing tool feed mechanism TF again as taught above by moving the reversible switch 76 so as to close the contacts R whereby the rotation of the motor 63 and the screw 66 are reversed to traverse the slide 14 together with transversely movable slide 12, the follower 40, the truing tool carrier 11, truing tool 10, and the speed control pinions 108, 73 and rack bar 72 toward the left.

Although specific embodiments of the invention have been described and diagrammatically illustrated herein, it should be noted that alternative arrangements and embodiments may also be feasible without departing from the spirit of the invention or the scope of the following claims directed thereto. lt is clear that the apparatus and method hereinbefore described represent a distinct advance in the art which is capable of benefiting industry generally.

What is claimed is:

1. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation;

means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face;

means for dressing the grinding face including ,a tool carrier movable toward and away from the axis of rotation,

a dressing tool on and movable with the tool carrier,

tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress and peripheral grinding face of the grinding wheel to a predetermined shape,

means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly,

means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises:

variable drive means operatively connected to the means for traversing the dressing tool; and

speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool as an inverse function of changes in the radial distance of the truing tool from the axis of rotation of the grinding wheel.

2. The combination according to claim 1 wherein the variable drive means for traversing the dressing tool comprises:

a reversible fluid motor operatively connected to the tool carrier means;

means for supplying and conveying fluid under pressure to drive the fluid motor; and

directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions.

3. The combination according to claim 1 wherein the variable drive means comprises:

a reversible variable speed electric motor having a drive shaft operatively connected to the tool carrier means;

means for supplying and conveying electrical energy to drive the electric motor; and

directional control means for selectively directingthe electrical energy to drive the reversible electric motor in opposite directions of rotation.

4. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation;

means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face;

means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation,

a dressing tool on and movable with the'tool carrier,

tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape,

means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly,

means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises:

variable drive means operatively connected to the means for traversing the dressing tool;

speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantially constant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel; said variable drive means for traversing the dressing tool comprises: a reversible fluid motoroperatively connected to the tool carrier means; means for supplying and conveying fluid under pressure to drive the fluid motor; and directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions; and said speed control means comprises: a fluid flow control valve having a valve housing, an inlet port, and an outlet port spaced from the inlet port; a speed control member in and movable relative to the housing and having an orifice of constantly varing area extending between the inlet and the outlet ports; and actuating means connected to and responsive to radial movement and position of the tool carrier and the dressing tool relative to the axis of rotation for causing relative movement between the housing and the speed control member and changing the area of the orifice, flow of fluid through the orifice, and the speed of the fluid motor in response to the radial movement and position of the dressing tool relative to the axis of rotation. 5. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape,

means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly,

means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises:

variable drive means operatively connected to the means for traversing the dressing tool;

speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantially constant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel, said variable drive means for traversing the dressing tool comprises: a reversible fluid motor operatively connected to the tool carrier means; means for supplying and conveying fluid under pressureto drive the fluid motor; and directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions; and said speed control means comprises: a fluid flow control valve having a valve housing, fixed against radial movement relative to the axis of rotation, attached to and movable with the tool carrier means in the longitudinal direction having a bore in the housing, an inlet port in the housing leading into the bore, an outlet port in the housing leading from the bore; a speed control member movable in the bore relative to the housing and having a slot of constantly varying depth extending between the inlet and outlet ports in the housing; a needle member in the valve housing having an end portion extending into the slot and providing an orifice between the speed control member and the needle of a size determined by the position of the speed control member relative to the needle and through which the fluid flows at a rate determining the speed of the fluid motor and the dressing tool across the grinding face; and actuating means connected to the tool carrier and the speed control member for shifting the speed control member relative to the needle and changing the size of the orifice in response to the radial movement and position of the tool carrier and dressing tool relative to the axis of rotation. 6. The combination according to claim 5 wherein the actuating means comprises:

a rack bar with gear teeth thereon'fixed to and movable with the tool carrier relative to the axis of rotation of the grinding wheel;

a drive gear with gear teeth meshing with the gear teeth on the rack bar and rotatably mounted on the housing; and

a driven gear fixed to and rotatably driven by the drive gear and having gear teeth meshing with rack teeth on the speed control member.

7. The combination according to claim 6 wherein the reversible fluid motor is a linear fluid motor comprising:

a cylinder,

a piston slideable in the cylinder; and

a piston rod connected to the piston and the tool carrier means.

8. The combination according to claim 6 wherein the variable drive means comprises:

a reversible rotary fluid motor having a rotatable drive shaft; and a rotatable feed screw coupled to the drive shaft and threadedly engaging tool carrier means for traversing the dressing tool across the grinding face. 9. The combination according to claim 8 wherein the variable drive means further comprises:

a gear reduction mechanism coupled to the drive shaft and the feed screw. 10. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of-the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape, means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly, means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises: variable drive means operatively connected to the means for traversing the dressing tool; speed control means operatively connected to the variable drive means and responsive to raidal movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantiallyconstant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel; said variable drive means comprises:

a reversible variable speed electric motor having a drive shaft operatively connected to the tool carrier means; means for supplying and conveying electrical energy to drive the electric motor; and directional control means for selectively directing the electrical energy to drive the reversible electric motor in opposite directions of rotation; and said speed control means comprises:

an electrical control circuit; a rheostat connected to the electrical circuit and having a variable resistance element connected electrically to the electrical motor, and

a movable contact element engaging and movable relative to the resistance element;

actuating means connected to the tool carrier and the movable contact element for shifting the movable contact element relative to the resistance element to vary the resistance and rotational speed of the electric motor and the dressing tool across the grinding face in response to the radial movement and position of the tool car rier and dressing tool relative to the axis of rotation.

11. The combination according to claim 10 wherein the variable drive means further comprises:

a rotatable feed screw coupled to the drive shaft of the electric motor and threadedly engaging the tool carrier means for traversing the dressing tool across the grinding face.

12. The combination according to claim 11 wherein the variable drive means further comprises:

a gear reduction mechanism coupled to and situated between the drive shaft of the electric motor and the feed screw.-

13. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as an inverse function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.

14. An apparatus as set forth in claim 13 wherein said motor means includes a fluid motor, and said control means includes conduit means for conducting fluid to andfrom said fluid motor and means for varying the rate of fluid flow through said conduit means as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.

15. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, said motor means including a fluid motor, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel, said control means including conduit means for conducting fluid to and from said fluid motor and means for varying the rate of fluid flow through said conduit means as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding-wheel, said means for varying the rate of fluid 'flow through said conduit means includes means for defining an orifice of variable cross-sectional area and means for varying the cross-sectional area of said orifice as a function of variations in th distance between the dressing tool and the axis of rotation of the grinding wheel.

16. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, said motor means including an electrical motor, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel, said control means including electrical circuit means for conducting electrical energy to said electric motor and means for varying the rate at which electrical energy is conducted to said electrical motor as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.

17. An apparatus as set forth in claim 16 wherein said means for varying the rate at which electrical energy is conducted to said electrical motor includes a rheostat and means for actuating said rheostat to an extent which varies as a function of variations in the distance between the dressing'tool and the axis of rotation of the grinding wheel.

18. An apparatus for dressing the peripheral grinding face of a circular grinding wheel with a dressing tool, apparatus comprising tool holder means for supporting the dressing tool for movement toward and away from a central axis of the grinding wheel and for supporting the dressing tool for movement along a path extending parallel to the face of the grinding wheel, first motor means for rotating the grinding wheel about its central axis, first control means for varying the rotational speed at which said first motor means rotates the grinding wheel as a function of variations in the diameter of the grinding wheel to maintain the peripheral speed of the face of the grinding wheel substantially constant, second motor means for moving said toolholder means along said path to move dressing tool across the face of the grinding wheel, and second control means for varying the speed at which said second motor means moves said toolholder means and dressing tool across the face of the grinding wheel as a function of variations in the diameter of the grinding wheel to maintain a substantially uniform finish on the face of the grinding wheel with changes in diameter of the grinding wheel.

19. A method of repeatedly dressing a substantially constant uniform surface finish on a peripheral grinding face of a circular grinding wheel, said method comprising the steps of rotating the grinding wheel about an axis of rotation, repeatedly dressing the grinding wheel by repeatedly moving a dressing tool transversely across the face of the grinding wheel while it is being rotated, maintaining the peripheral speed of the grinding wheel face constant as the diameter of the grinding wheel decreases due to the repeated dressing of the grinding wheel by increasing the angular velocity of rotation of the grinding wheel as the grinding wheel diameter decreases, and maintaining a substantially constant uniform surface finish on the face of the grinding wheel as the diameter of the grinding wheel decreases and the angular velocity of rotation of the grinding wheel increases by increasing the speed at which the dressing tool is moved across the face of the grinding wheel as wheel. 

1. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress and peripheral grinding face of the grinding wheel to a predetermined shape, means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly, means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises: variable drive means operatively connected to the means for traversing the dressing tool; and speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed And varying the speed of the variable means for traversing the truing tool as an inverse function of changes in the radial distance of the truing tool from the axis of rotation of the grinding wheel.
 2. The combination according to claim 1 wherein the variable drive means for traversing the dressing tool comprises: a reversible fluid motor operatively connected to the tool carrier means; means for supplying and conveying fluid under pressure to drive the fluid motor; and directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions.
 3. The combination according to claim 1 wherein the variable drive means comprises: a reversible variable speed electric motor having a drive shaft operatively connected to the tool carrier means; means for supplying and conveying electrical energy to drive the electric motor; and directional control means for selectively directing the electrical energy to drive the reversible electric motor in opposite directions of rotation.
 4. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape, means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly, means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises: variable drive means operatively connected to the means for traversing the dressing tool; speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantially constant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel; said variable drive means for traversing the dressing tool comprises: a reversible fluid motor operatively connected to the tool carrier means; means for supplying and conveying fluid under pressure to drive the fluid motor; and directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions; and said speed control means comprises: a fluid flow control valve having a valve housing, an inlet port, and an outlet port spaced from the inlet port; a speed control member in and movable relative to the housing and having an orifice of constantly varing area extending between the inlet and the outlet ports; and actuating means connected to and responsive to radial movement and position of the tool carrier and the dressing tool relative to the axis of rotation for causing relative movement between the housing and the speed control member and changing the area of the orifice, flow of fluid through the orifice, and tHe speed of the fluid motor in response to the radial movement and position of the dressing tool relative to the axis of rotation.
 5. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape, means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly, means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises: variable drive means operatively connected to the means for traversing the dressing tool; speed control means operatively connected to the variable drive means and responsive to radial movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantially constant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel, said variable drive means for traversing the dressing tool comprises: a reversible fluid motor operatively connected to the tool carrier means; means for supplying and conveying fluid under pressure to drive the fluid motor; and directional control means for selectively directing the fluid under pressure to drive the reversible fluid motor in opposite directions; and said speed control means comprises: a fluid flow control valve having a valve housing, fixed against radial movement relative to the axis of rotation, attached to and movable with the tool carrier means in the longitudinal direction having a bore in the housing, an inlet port in the housing leading into the bore, an outlet port in the housing leading from the bore; a speed control member movable in the bore relative to the housing and having a slot of constantly varying depth extending between the inlet and outlet ports in the housing; a needle member in the valve housing having an end portion extending into the slot and providing an orifice between the speed control member and the needle of a size determined by the position of the speed control member relative to the needle and through which the fluid flows at a rate determining the speed of the fluid motor and the dressing tool across the grinding face; and actuating means connected to the tool carrier and the speed control member for shifting the speed control member relative to the needle and changing the size of the orifice in response to the radial movement and position of the tool carrier and dressing tool relative to the axis of rotation.
 6. The combination according to claim 5 wherein the actuating means comprises: a rack bar with gear teeth thereon fixed to and movable with the tool carrier relative to the axis of rotation of the grinding wheel; a drive gear with gear teeth meshing with the gear teeth on the rack bar and rotatably mounted on the housing; and a driven gear fixed to and rotatably driven by the drive gear and having gear teeth meshing with rack teeth on the speed control member.
 7. The combination according to claim 6 wherein the reversible fluid motor is a linear fluid motor comprising: a cylinder, a piston slideable in the cylinder; and a piston rod connected to the piston and the tool carrier means.
 8. The combination according to claim 6 wherein the variable drive means comprises: a reversible rotary fluid motor having a rotatable drive shaft; and a rotatable feed screw coupled to the drive shaft and threadedly engaging tool carrier means for traversing the dressing tool across the grinding face.
 9. The combination according to claim 8 wherein the variable drive means further comprises: a gear reduction mechanism coupled to the drive shaft and the feed screw.
 10. In combination with a grinding machine having a grinding wheel with a peripheral grinding face rotatably supported for rotation about an axis of rotation; means for rotating and progressively changing angular velocity of the grinding wheel in accordance with changing grinding wheel diameter to maintain a substantially constant peripheral surface speed of the grinding face; means for dressing the grinding face including a tool carrier movable toward and away from the axis of rotation, a dressing tool on and movable with the tool carrier, tool carrier means for supporting the tool carrier and the dressing tool movable relative to and into operative relation to dress the peripheral grinding face of the grinding wheel to a predetermined shape, means for feeding the tool carrier and the dressing tool a predetermined increment relative to the tool carrier means, the grinding face, and toward the axis of rotation to dress and thereby reduce the diameter of the grinding wheel accordingly, means for traversing the tool carrier means and the dressing tool across the grinding face in a longitudinal direction of the axis of rotation of the grinding wheel; wherein the improvement comprises: variable drive means operatively connected to the means for traversing the dressing tool; speed control means operatively connected to the variable drive means and responsive to raidal movement and distance of the dressing tool from the axis of rotation of the grinding wheel for determining a speed and varying the speed of the variable means for traversing the truing tool to maintain and repeatedly produce a substantially constant uniformly dressed surface finish on the grinding face during the life of the wheel in accordance with the changes in the radial distance of the truing tool from the axis of rotation and diameter of the grinding wheel; said variable drive means comprises: a reversible variable speed electric motor having a drive shaft operatively connected to the tool carrier means; means for supplying and conveying electrical energy to drive the electric motor; and directional control means for selectively directing the electrical energy to drive the reversible electric motor in opposite directions of rotation; and said speed control means comprises: an electrical control circuit; a rheostat connected to the electrical circuit and having a variable resistance element connected electrically to the electrical motor, and a movable contact element engaging and movable relative to the resistance element; actuating means connected to the tool carrier and the movable contact element for shifting the movable contact element relative to the resistance element to vary the resistance and rotational speed of the electric motor and the dressing tool across the grinding face in response to the radial movement and position of the tool carrier and dressing tool relative to the axis of rotation.
 11. The combination according to claim 10 wherein the variable drive means further comprises: a rotatable feed screw coupled to the drive shaft of The electric motor and threadedly engaging the tool carrier means for traversing the dressing tool across the grinding face.
 12. The combination according to claim 11 wherein the variable drive means further comprises: a gear reduction mechanism coupled to and situated between the drive shaft of the electric motor and the feed screw.
 13. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as an inverse function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.
 14. An apparatus as set forth in claim 13 wherein said motor means includes a fluid motor, and said control means includes conduit means for conducting fluid to and from said fluid motor and means for varying the rate of fluid flow through said conduit means as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.
 15. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, said motor means including a fluid motor, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel, said control means including conduit means for conducting fluid to and from said fluid motor and means for varying the rate of fluid flow through said conduit means as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel, said means for varying the rate of fluid flow through said conduit means includes means for defining an orifice of variable cross-sectional area and means for varying the cross-sectional area of said orifice as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.
 16. An apparatus for dressing the peripheral grinding face of a grinding wheel with a dressing tool, said apparatus comprising means for rotating the grinding wheel about its central axis, motor means for moving the dressing tool across the face of the grinding wheel as it is being rotated, said motor means including an electrical motor, and control means for varying the speed at which said motor means moves the dressing tool across the face of the grinding wheel as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel, said control means including electrical circuit means for conducting electrical energy to said electric motor and means for varying the rate at which electrical energy is conducted to said electrical motor as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.
 17. An apparatus as set forth in claim 16 wherein said means for varying the rate at which electrical energy is conducted to said electrical motor includes a rheostat and means for actuating said rheostat to an extent which varies as a function of variations in the distance between the dressing tool and the axis of rotation of the grinding wheel.
 18. An apparatus for dressing the peripheral grinding face of a circular grinding wheel with a dressing tool, apparatus comprising tool holder means for supporting the dressing tool for movement toward and away from a central axis of the grinding wheel and for supporting the dressing tool for movement along a path extending parallel to the face of the grinding wheel, first motor means for rotating the grinding wheel about its central axis, first control means for varying the rotational speed at which said first motor means rotates the grinding wheel as a function of variations in the diameter of the grinding wheel to maintain the peripheral speed of the face of the grinding wheel substantially constant, second motor means for moving said toolholder means along said path to move dressing tool across the face of the grinding wheel, and second control means for varying the speed at which said second motor means moves said toolholder means and dressing tool across the face of the grinding wheel as a function of variations in the diameter of the grinding wheel to maintain a substantially uniform finish on the face of the grinding wheel with changes in diameter of the grinding wheel.
 19. A method of repeatedly dressing a substantially constant uniform surface finish on a peripheral grinding face of a circular grinding wheel, said method comprising the steps of rotating the grinding wheel about an axis of rotation, repeatedly dressing the grinding wheel by repeatedly moving a dressing tool transversely across the face of the grinding wheel while it is being rotated, maintaining the peripheral speed of the grinding wheel face constant as the diameter of the grinding wheel decreases due to the repeated dressing of the grinding wheel by increasing the angular velocity of rotation of the grinding wheel as the grinding wheel diameter decreases, and maintaining a substantially constant uniform surface finish on the face of the grinding wheel as the diameter of the grinding wheel decreases and the angular velocity of rotation of the grinding wheel increases by increasing the speed at which the dressing tool is moved across the face of the grinding wheel as a function of variations in the diameter of the grinding wheel. 